Digital photography has been growing rapidly for several years and the general public now has access to efficient and reasonably priced digital cameras. Therefore people are seeking to be able to produce photographic prints from a simple computer and its printer with the best possible quality.
Many printers, especially those linked to personal office automation, use the inkjet printing technique. There are two major families of inkjet printing techniques: continuous jet and drop-on-demand.
Continuous jet is the simpler system. Pressurized ink (typically 3.105 Pa) is forced through one or more nozzles so that the ink forms a flow of droplets. Regular pressure pulses ensure regular sizes and spaces between droplets and can be generated using, for example, a piezoelectric crystal with high frequency (up to 1 MHz) alternating current (AC) power supply. So that a message can be printed using a single nozzle, every drop must be individually controlled and directed. Electrostatic energy is used for this: an electrode is placed around the inkjet at the place where drops form. The jet is charged by induction and every drop henceforth carries a charge whose value depends on the applied voltage. The drops then pass between two deflecting plates charged with the opposite sign and then follow a given direction, the amplitude of the movement being proportional to the charge carried by each of them. To prevent other drops from reaching the paper they are left uncharged, so instead of going to the support they continue their path without being deflected and go directly into a container. The ink is then filtered and can be reused. Alternatively, deflection of ink droplets can be effected by selectively controlling the size of the drop to allow them to be sorted by selective deflection using a stream of air.
The other category of inkjet printing is drop-on-demand (DOD). This is the most commonly used inkjet printing method in the home and office environment. With this method the pressure in the ink cartridge is not maintained constant but is applied when a character has to be formed. In one widespread system there is a row of open nozzles, each of them being activated with a piezoelectric crystal. The ink contained in the head is given a pulse: the piezo element contracts with an electric voltage which causes a decrease of volume, leading to the expulsion of the drop by the nozzle. When the element resumes its initial shape, it pumps in the reservoir the ink necessary for new printings. The row of nozzles is thus used to generate a column matrix so that no deflection of the drop is necessary. One variation of this system consists in replacing the piezoelectric crystals by small heating elements behind each nozzle. The drops are ejected following the forming of bubbles of solvent vapour. The volume increase enables the expulsion of the drop. Finally, there is a pulsed inkjet system in which the ink is solid at ambient temperature. The printhead thus has to be heated so that the ink liquefies and can print. This enables rapid drying on a wider range of products than conventional systems.
There now exist new “inkjet” printers capable of producing photographic images of excellent quality. However, they cannot supply good proofs if inferior quality printing paper is used. The choice of printing paper is fundamental for the quality of the obtained image. The printing paper should combine the following properties: high quality printed image, rapid drying after printing, good dye keeping over time, smooth appearance and high gloss.
In general, the printing paper comprises a support coated with one or more layers according to the properties required. It is possible, for example, to apply on a support a primary attachment layer, an absorbent layer, an ink dye-fixing layer, and a protective layer or surface layer to provide the glossiness of the recording element. A single layer may provide more than one of these functions. The absorbent layer absorbs the liquid part of the water-based ink composition after creation of the image. Elimination of the liquid reduces the risk of ink migration at the surface. The ink dye-fixing layer prevents any dye loss into the fibres of the paper base to obtain good colour saturation, whilst preventing excess ink that would encourage the increase in size of the printing dots and reduce the image quality. The absorbent layer and dye-fixing layer can also constitute a single ink-receiving layer ensuring both functions. The protective layer is designed to ensure protection against fingerprints and the pressure marks of the printer feed rollers. The ink-receiving layer comprises a binder, a receiving agent and various additives. The purpose of the receiving agent is to fix the dyes in the printing paper. The best-known inorganic receivers are fumed alumina, fumed silica, colloidal silica and boehmite. For example, EP-A-0 976 571 and EP-A-1 162 076 describe recording elements for inkjet printing in which the ink-receiving layer contains, as inorganic receivers, Ludox™ CL (colloidal silica) marketed by Grace Corporation, or Dispal™ (colloidal boehmite), marketed by Sasol. However, printing paper comprising an ink-receiving layer containing such inorganic receivers can have poor image stability over time, which is demonstrated by a loss of colour density.
To meet the new requirements of the market in terms of photographic quality, printing speed and colour stability, it is necessary to be able to offer a new inkjet recording element having the properties as defined above, more particularly good dye-keeping properties, whilst keeping instant dryness.
Naito et al. in published application JP 59-103789 disclose a plain paper for inkjet recording in which the sizing agent or surface-coating agent comprises a filler including a clay mineral modified by an organic substance. Plain paper does not provide a photographic quality print.
Abe et al. in U.S. Pat. No. 5,342,876 describe inkjet recording papers coated with aluminium, zinc and magnesium phyllosilicates in a poly(vinyl alcohol) binder, providing improved resistance to fading of image dyes exposed to UV light. These materials are made in the presence of 30% polyacrylamide with respect to silica, but do not include any organic moiety covalently bound to silicon.
Nakano et al. in U.S. Pat. No. 5,919,559 describe an inkjet recording sheet comprising particles of a layered silicate modified with an organic treating agent such as a poly(oxyethylene)trialkylammonium chloride, the preparation of which is described in JP 06-287014. Here an alkylammonium ion is intercalated between the layers, but does not form a covalent bond with silicon. No improvement in resistance to dye fade is demonstrated.
Iguchi et al. in JP 2003-080832 disclose a coating agent for an inkjet recording sheet comprising silsesquioxane particles represented by the structural unit RSiO(3/2). The particles do not contain a metal and no improvement of dye-fade resistance is disclosed.
Kapusniak et al. in US 2005/0158486 disclose an inkjet recording element comprising particles of aluminosilicate for improved high humidity keeping. The particles do not contain an organic moiety and no mention is made of improved resistance to ozone fade. The recording element is swellable, not porous.
Chen in US 2006/0083870 discloses a porous ink-receiving layer comprising amine-functionalized particulates, which may be clays. The amine-functionalized particles are intended to covalently couple with epoxy-modified particles to provide a binding function and reduce cracking. No disclosure of improved resistance to ozone fade is made.
Bringley et al. in publication WO 2005/009747 describe porous inkjet media containing core/shell particles, wherein the shell of the particles is an oligomeric or polymeric aluminosilicate complex or aluminosilicate particulate and the core is organic or inorganic. Core materials having a negative surface charge, such as silica, are preferred. The resistance to fading of image dyes printed on the medium is improved, compared with standard particles of silica or alumina. The particles are not organically modified.
Pinnavia et al. in U.S. Pat. No. 7,132,165 disclose novel lamellar mesoporous silica compositions which contain functional inorganic elements and organic functional groups, prepared using gemini amine surfactants as template or structure-directing agents. It is stated that such a material could find a catalytic application but there is no disclosure of use in an inkjet-related application.
WO 2004/039724 discloses an aluminosilicate polymer obtained by treating an unmodified mixed aluminium and silicon alkoxide with an aqueous alkali, stirring the resulting mixture for sufficient time for a polymer to form and eliminating the by-products. The mixed aluminium and silicon alkoxide is preferably formed by reaction of, for example, aluminium chloride with a silicon alkoxide, such as silicon tetraethoxide.
Analogously WO 2004/009494 discloses a hybrid aluminosilicate polymer obtained by treating a mixed aluminium and silicon alkoxide, the silicon alkoxide having both hydrolyzable and non-hydrolyzable substituents, with an aqueous alkali, stirring the resulting mixture for sufficient time for a polymer to form and eliminating the by-products. The mixed aluminium and silicon alkoxide is preferably formed by reaction of, for example, aluminium chloride with an unmodified silicon alkoxide, such as tetraethoxysilane, and a modified silicon alkoxide, such as methyl triethoxysilane.
In both the above specifications, the preparation of the aluminosilicate requires the molar concentration of aluminium to be less than 0.3, the molar ratio of aluminium to silicate to be from 1 to 3.6 and the alkali to aluminium molar ratio to be from 2.3 to 3. The reactions are conducted in the presence of silanol groups, such as silica beads. Aluminosilicate polymers made according to these methods find particular utility as components of ink-receiving layer of inkjet receiver having improved dye-keeping properties and gloss.
There is a continuing need for an inkjet receiver that has improved colour stability on printing and improved keeping to enable longevity of photographic prints and colour documents prepared via inkjet printing.